Magnetic resonance imaging system and method

ABSTRACT

The present invention relates to a magnetic resonance imaging system that includes a stationary electromagnet, a patient support for maintaining a patient in a standing or seated position, and an actuator for raising and lowering the patient relative to a magnetic field of the electromagnet such that the patient is located within the magnetic field.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/118,665,filed Jul. 17, 1998, now U.S. Pat. No. 6,697,659. The aforementionedapplication Ser. No. 09/118,665 is itself a divisional of applicationSer. No. 08/455,074, filed May 31, 1995, now U.S. Pat. No. 6,671,537.The aforementioned application Ser. No. 08/455,074 is a divisional ofapplication Ser. No. 08/221,848, filed Apr. 1, 1994, now U.S. Pat. No.5,577,503. The aforementioned application Ser. No. 08/221,848 is itselfa divisional of application Ser. No. 07/802,358, filed Dec. 4, 1991, nowU.S. Pat. No. 5,349,956.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and method for use inmedical imaging. More particularly, the present invention relates toapparatus and method for positioning a patient and/or a secondaryimaging coil inside a primary imaging coil.

In magnetic resonance imaging, a patient is placed inside a coil (the“primary” coil) which is large enough in diameter to receive the patientwhile he is lying prone on a table slidable into and out of the coil. Aselected portion of the patient is then imaged by the use ofelectromagnetic radiation from the primary coil.

It is known to place smaller coils, called surface or volume coils, inclose proximity to the specific part of the patient to be imaged, suchas the neck, spine, or knee. These coils, referred to herein assecondary coils, are used to increase resolution by having a coil closerto the part to be imaged. It is essential to place the secondary coil ina particular orientation relative to the electromagnetic field generatedby the primary coil.

Current imaging systems can only take images while a patient is in oneparticular position. One known device allows the patient to move hisknee joint to different selected positions while the patient is in theprimary coil. This device requires the patient to lie face down in theprimary coil, which is extremely uncomfortable for the extended periodof time required to image properly, especially in the close, almostclaustrophobic confines of a primary MRI coil.

SUMMARY OF THE INVENTION

The present invention is an apparatus and method for use in medicalimaging. The present invention provides a system to simulate within animaging coil normal movements of body parts such as joints, and toimprove imaging of soft tissue and bony parts as compared to a staticsystem in which images are taken of a joint in only one position.

In accordance with a first aspect of the present invention, there isprovided controlled motion of an extremity, while in an imaging coil,either patient directed or operator directed. A joint or body part ismoved into various positions in multiple planes within its range ofmotion while a series of images are taken of the joint in the differentpositions. These individual images may then be collated into a cineformat to effectively show the joint in motion. Thus, the presentinvention allows for studying a joint in motion and also allows forstudying a joint or other body part at any positions within its range ofmotion allowable within the confines of the primary coil.

In accordance with a second aspect of the present invention, a surfaceor volume coil (referred to herein as a secondary coil) is coupled formovement with the joint or body part. The secondary coil is maintainedin the proper spatial relationship with the primary coil'selectromagnetic field. Keeping the secondary coil as close as possibleto the joint or tissue being imaged, while moving the joint or bodypart, provides greatly enhanced resolution and more detail in the finalimage.

Thus, to illustrate these first two aspects of the invention in kneeimaging, the knee is fixed by holding the upper and lower legs withcuffs and a secondary coil is placed around the knee itself. The knee isthen imaged at 0 degrees by using the primary and secondary coils. Theknee is then flexed (either by the patient or the operator), and thesecondary coil moves with the knee. The knee is progressively movedthrough various positions within its range of motion as limited only bythe size of the primary coil. Images are taken at each position. Theimages may then be collated and shown in sequence to visualize themovement of the knee joint, or may be studied individually to study thejoint at each position.

Similar systems are available for other joints, the back, neck, etc.These systems all are preferably provided as mechanisms usable withexisting imaging tables to reduce cost. Alternatively, some of these maybe built into a new imaging table.

Coupling a surface coil for movement with the extremity provides thenecessary detail in the images, even with a larger primary coil, whichis not available with present systems. Accordingly, it is possible touse a larger diameter primary coil, allowing this increased range ofmovement, without the degradation in image quality which would beexpected from the increased coil size. For example, the knee could beflexed through its entire range of motion to allow optimum imaging ofthe knee joint. This is currently impossible with the known smallprimary coils which only allow about 50 degrees of flexion.

In accordance with another aspect of the present invention, traction isapplied to a joint being imaged, in order to load the joint. This cansimulate normal loading of a joint. Distracting a joint can also allow abetter view of the parts of the joint and thus an increased imagingbenefit. It can also allow simulation of normal loading of a joint, suchas when carrying a heavy object or performing an athletic orwork-related task. This feature is not available with present imagingapparatus. Traction can also be applied to a joint being imaged when thejoint is in various positions, to simulate normal loading of a jointwithin its range of motion. Again, this feature is not available withpresent imaging apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to one skilled in the art upon a consideration of the followingdescription of the invention with reference to the accompanyingdrawings, wherein:

FIG. 1A is a perspective view of a magnetic resonance imaginginstallation including a patient support table constructed in accordancewith the present invention;

FIG. 1B is a view of the table of FIG. 1A in another condition;

FIG. 1C is a view of the table of FIG. 1A in yet another condition;

FIG. 2 is an enlarged view of a back imaging platform of the table ofFIG. 1A;

FIG. 3 illustrates the platform of FIG. 2 in a raised condition;

FIG. 4 illustrates the platform of FIG. 2 in a lowered condition;

FIG. 5 is a view similar to FIG. 2 showing a different actuatingmechanism for the back imaging platform;

FIG. 6 illustrates the platform of FIG. 5 in a raised condition;

FIG. 7 illustrates the platform of FIG. 5 in a lowered condition;

FIG. 8 is an enlarged view of a knee imaging platform portion of thetable of FIG. 1;

FIG. 9 illustrates the platform of FIG. 8 in a raised condition;

FIG. 10 is a view similar to FIG. 8 and showing a different actuatingmechanism for the knee platform;

FIG. 11 illustrates the platform of FIG. 10 in a raised condition;

FIG. 12 is an enlarged view of a neck imaging platform portion of thetable of FIG. 1A;

FIG. 13 illustrates the platform of FIG. 12 in a raised condition;

FIG. 14 illustrates the platform of FIG. 12 in a lowered condition;

FIG. 15 is a view similar to FIG. 12 illustrating a different actuatingmechanism for the neck platform;

FIG. 16 illustrates the platform of FIG. 15 in a raised condition;

FIG. 17 illustrates the platform of FIG. 15 in a lowered condition;

FIG. 18 illustrates the platform of FIG. 15 with a foot rest attachedfor use in ankle imaging;

FIG. 19 illustrates the platform of FIG. 18 in a raised condition;

FIG. 20 illustrates the platform of FIG. 18 in a lowered condition;

FIG. 21 illustrates the platform of FIG. 18 with a different actuatingmechanism;

FIG. 22 illustrates the platform of FIG. 21 in a raised condition;

FIG. 23 illustrates the platform of FIG. 21 in a lowered condition;

FIG. 24 is a top plan view of a shoulder positioning apparatus inaccordance with the present invention shown attached to an imaging tablewith a shoulder coil;

FIG. 25 is a side view of the apparatus of FIG. 24;

FIG. 25A is a partial end view of the positioning apparatus of FIG. 25taken along line 25A—25A of FIG. 24;

FIG. 26 is an enlarged perspective view of a portion of the positioningapparatus of FIG. 24;

FIG. 26A is a view similar to FIG. 26 showing an alternate indexingmechanism;

FIG. 27 is a top plan view of a head and neck positioning apparatus;

FIG. 28 is an end view of the apparatus of FIG. 27;

FIG. 29 is a perspective view of the apparatus of FIG. 27;

FIG. 30 is a top plan view of a wrist imaging apparatus embodying thepresent invention and including a hand cuff;

FIG. 31 illustrates the apparatus of FIG. 30 in a different condition;

FIG. 32 illustrates the apparatus of FIG. 30 with a different hand cuff;

FIG. 33 is an end view of the apparatus of FIG. 30;

FIG. 34 is an enlarged end view of the hand cuff of the apparatus ofFIG. 30;

FIG. 35 is a side view of the hand cuff of FIG. 34;

FIG. 36 is a bottom plan view of the hand cuff of FIG. 34;

FIG. 37 is a top plan view of an independent patient directed kneepositioning apparatus embodying the present invention;

FIG. 38 is a side view of the apparatus of FIG. 37;

FIG. 39 is a view similar to FIG. 38 with the apparatus in a raisedcondition;

FIG. 40 is a view similar to FIG. 39 with an optional distractionmechanism;

FIG. 41 is a schematic view showing the dimensions of a known primaryMRI coil;

FIG. 42 is a schematic view showing the dimensions of a larger sizedprimary MRI coil embodying the present invention; and

FIG. 43 is a schematic view of a vertically extending primary MRI coilin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a patient support table 10 for supporting a patient(not shown) during imaging inside a primary coil 12 of a magneticresonance imaging installation. The table 10 is supported on tracks 14and a floor support 16 for sliding longitudinal movement into and out ofthe coil 12.

The table 10 has an upper major side surface 20 extending between a headend 22 and a foot end 24. The table also has a right side 26 and a leftside 28.

The table 10 includes a neck imaging platform indicated generally at 30.The neck imaging platform 30 includes a movable head panel 32 adjacentto a recess 34 for receiving a secondary imaging coil such as a cervicalspine coil.

The table 10 includes a back imaging platform indicated generally at 40.The back imaging platform 40 includes a movable upper back panel 42 anda movable lower back panel 44. A movable center section 46 of the backimaging platform 40 includes a recessed panel 48 for receiving asecondary back imaging coil. The recessed panel 48 is located between aleft side back panel 50 and a right side back panel 52.

The table 10 also includes a pair of knee imaging platforms 54 and 56.The left knee imaging platform 54 includes a movable upper left kneepanel 58, a movable lower left knee panel 60 and, between them, arecessed panel 62 for receiving a left knee secondary imaging coil.Similarly, the right knee imaging platform 56 includes a movable upperright knee panel 64, a movable lower right knee panel 66, and a movablerecessed panel 68 for receiving a right knee secondary imaging coil.

As can be seen in FIGS. 1A, 1B and 1C, the head panel 32 is movablebetween a plurality of positions relative to the upper major sidesurface 20 of the table 1A. In FIG. 1A, the head panel 32 is in aposition level with the upper major side surface 20 of the table 10. InFIG. 1B, the head panel 32 is raised above the upper major side surfaceof the table 10. In FIG. 1C, the head panel 32 is lowered below theupper major side surface 20 of the table 10. With a patient's head onthe head panel 32 and by moving the panel 32 in a manner as describedbelow, a patient's cervical spine can be imaged in a variety ofpositions, by a coil placed on the recess panel 34.

Similarly, the back imaging platform 40 is movable between a pluralityof positions relative to the upper major side surface 20 of the table10, to image the back in varying positions. In FIG. 1A, the back imagingplatform is level or flush with the upper major side surface 20 of thetable 10. In FIG. 1B, the back imaging platform 40 is raised up abovethe upper major side surface 20 of the table 10, in order tohyper-extend the spine of a patient lying on the table 10. In FIG. 1C,the back imaging platform 40 is lowered below the upper major sidesurface 20 of the table 10, in order to flex the spine. Thus, by movingthe back platform 40 between these various positions, in a manner to bedescribed below, the back can be imaged in a plurality of differentpositions, rather than only in the one flat position possible with aflat table.

Similarly, the left and right knee imaging platforms 54 and 56,respectively, are movable between a plurality of positions relative tothe upper major side surface 20 of the table 10. In FIGS. 1A and 1C, theplatforms 54 and 56 are illustrated flush with the upper major sidesurface 20 of the table 10. In FIG. 1B, the left knee imaging platform54 is illustrated as raised up above the upper major side surface 20 ofthe table 10. Both knee platforms 56 and 66 are each independentlymovable above or below the upper major side surface 20 of the table 10.By thus moving a knee platform among these various positions, in amanner to be described below, a knee joint can be imaged in a pluralityof positions, as opposed to the one single position available with aflat or nonmovable table.

FIGS. 2-4 illustrate in more detail the back imaging platform 40 and amechanism for actuating same. These are exemplary of the other platformsand their actuating mechanisms. The fixed portion 70 of the table 10includes a track 72 receiving mounting rollers 74 and 76 for the upperback panel 42 and lower back panel 44, respectively. The upper backpanel 42 is pivotally mounted at 78 to the center back section 46. Thelower back panel 44 is similarly pivotally mounted at 80 to the centerback section 46.

An inflatable bladder 82 extends between the center back section 46 andthe lower panel 84 of the table 10. The inflatable bladder 82 issupplied with fluid through a fluid supply line 86 extending along thetable 10. Fluid under pressure, preferably air, is supplied to thebladder 82 through the line 86 by means not shown such as a pump or ahigh pressure air line as is commonly found in hospitals, etc. Uponinflation of the bladder 82 from the condition shown in FIG. 2 to thecondition shown in FIG. 3, the bladder 82 extends longitudinally,raising the center back section 46 of the table 10 upwardly from themajor side surface 20 of the table 10. The pivotal connections 74, 76,78 and 80 allow the panels 42 and 44 to pivot upwardly, as illustratedin FIG. 3, sliding inwardly along the track 72.

Similarly, upon the reduction of pressure in the bladder 82, the bladder82 compresses axially in length to the condition shown in FIG. 4,lowering the center back section 46 below the major side surface 20 ofthe table 10. The state of inflation of the bladder 82 is selectivelycontrollable to position the center back section 46, relative to theupper major side surface 20 of the table 10, at any position between thefully extended position illustrated in FIG. 3 and the fully flexedposition illustrated in FIG. 4. The bladder 82 is preferably of abellows-type construction for increased strength and controlledmovement.

In FIGS. 2-4, a secondary coil 90 is illustrated as positioned on thecenter back section 46 of the table 10. The secondary coil 90 may be anyknown imaging coil designed for imaging a portion of the spine of apatient. As the center back section 46 moves up and down, the secondarycoil 90 moves with the back section 46. The secondary coil 90 isinitially (FIG. 2) parallel to the upper major side surface 20 of thetable 10, and stays with the center back section 46 in that parallelorientation throughout the entire range of movement of the back section46 and the coil 90. It should be noted that any type of secondary coileither known or to be developed in the future—surface coil, volume coil,etc.—can be used with the present invention.

With a patient (not shown) lying on the table 10, and a secondary coil90 positioned as shown, the patient's back can be imaged in a pluralityof orientations. If the table 10 is maintained in the position shown inFIG. 2, the patient's back is imaged in a flat position. If the table 10is moved to a raised position, as illustrated in FIG. 3, the patient'sback is imaged in an extended or hyper-extended condition. If the table10 is moved to a lowered condition, as illustrated in FIG. 4, thepatient's back is imaged in a flexed or hyper-flexed condition. Becausethe inflation state of the bladder 82 is selectively controllable andlockable at any state of inflation, the patient's back can be imagedwhen in any selected orientation within the full range of motion of theback imaging platform 40. Meanwhile, the secondary coil 90 moves withthe patient's back, always staying in close proximity thereto, tomaintain the high resolution sought by use of a secondary coil. Further,the secondary coil 90 always maintains its orientation parallel to theupper side surface 20 of the table 10, as is necessary for maximumresolution and clarity. Accordingly, it is seen that the presentinvention provides an apparatus for imaging the back of a patient, atany selected one or group of a plurality of orientations, while thepatient is maintained in the primary coil 10 (FIG. 1) of the MRI imagingapparatus, and without any extra effort on the part of the patient.

FIGS. 5-7 illustrate an alternate actuating mechanism for the centerback section 46 of the table 10. The actuating mechanism includes athreaded rod 100 rotatably mounted in a block 102 fixed to the bottompanel 84 of the table 10. The block 102 allows the rod 100 to rotate butprevents axial movement of the rod 100.

The rod 100 includes a first threaded portion 104 threadedly received ina floating mounting block 106 (FIG. 6). The floating block 106 has a pin108 secured thereto. The pin 108 is received in a slot 110 of an arm 112fixed to the upper back panel 42.

The rod 100 also includes a second threaded portion 114 which is ofopposite hand from the first threaded portion 104. The second threadedportion 114 extends through a floating mounting block 116 having a pin118 secured thereto. The pin 118 is received in a slot 120 of an arm 122fixed to the lower back panel 44.

An end portion 124 of the rod 100 projects axially from the foot end 24of the table 10. A drive means indicated schematically at 126 isattached to the rod 100. The drive means 126 may be a hand crank forrotating the rod 100 relative to the table 10. The drive means 126 mayalso be an electric motor or fluid drive mechanism for rotating the rod100. The drive means 126 is selectively controllable to rotate the rod100 to any given extent permitted by the actuating mechanism.

Upon actuation of the drive means 126, the rod 100 rotates relative tothe fixed mounting block 102 and the table 10. Because the threaded rodportions 104 and 114 are of opposite hand, upon rotation of the rod 100in one direction, the floating blocks 106 and 116 are moved inwardlytoward each other as illustrated in FIG. 6; and upon rotation of the rod100 in the opposite direction, the blocks 106 and 116 move axiallyoutwardly away from each other, as illustrated in FIG. 7.

Upon movement of the blocks 106 and 116 toward each other as illustratedin FIG. 6, the pins 108 and 118 pull the arms 112 and 122, respectively,from the position shown in FIG. 5 to the position shown in FIG. 6. Thiscauses the upper and lower back panels 42 and 44, respectively, to pivotand move inwardly along the track 72. This raises the center backsection 46 of the table 10 upwardly away from the major side surface 20of the table 10. The surface coil 90, as before, moves with the centerback section 46 and maintains its alignment parallel to the upper majorside surface 20 of the table 10.

Upon rotation of the rod 100 in the opposite direction, the blocks 106and 116 (FIG. 7) move axially outwardly away from each other, thuscausing the panels 42 and 44 to pivot to the position shown in FIG. 7.This drops the center back section 46 downwardly below the upper majorside surface 20 of the table 10, taking with it the secondary coil 90.

Accordingly, it is seen from FIGS. 5-7 that an alternate mechanism forpositioning the center back section 46 of the table 10, relative to theupper major side surface 20 of the table 10, is provided. With a patientlying on the upper major side surface 20 of the table 10, the patient'sback may thus be imaged in any selected one of a plurality of positionsbetween flexion and extension. Meanwhile, the secondary coil 90, ifused, moves with the patient's back to maintain high resolution, whilemaintaining its planar orientation relative to the upper major sidesurface 20 of the table 10.

FIGS. 8 and 9 illustrate operation of the right knee imaging platform 56of table 10. In this case, a knee secondary coil 130 is fixed bysuitable means such as straps or VELCRO.RTM. to the central panel 68 ofthe imaging platform 56. The central panel 68 is pivotally mountedbetween the upper right knee panel 64 and the lower right knee panel 66.A threaded rod 132, having oppositely threaded portions 134 and 136, isrotatably mounted in a fixed mounting block 138 to block axial movementof the rod 132. Connection means 140 (similar to the block 106, pin 108,and arm 112) movably connects the upper right knee panel 64 to thethreaded rod portion 134. Similar connection means 142 movably connectsthe lower right knee panel 66 to the rod threaded portion 136.

Upon rotation of the rod 132 by suitable drive means 144, in onedirection, the connection means 140 and 142 cause the panels 64 and 66,respectively, to pivot and lift the central panel 68 upwardly away fromthe upper major side surface 20 of the table 10. The knee coil 130 moveswith the panel 68 and stays in the correct planar orientation relativeto the primary coil. The patient's knee (not shown) also moves upwardlyaway from the major side surface 20, into a different orientation thanwhen the patient's knee is on the platform 56 when in the position shownin FIG. 8. Rotation of the rod 132 in the opposite direction causes thecentral panel 68 and knee coil 130 to drop below the upper major sidesurface 20 of the table 10, in a manner similar to that illustrated inFIG. 7 with the back section 46.

In the structure illustrated in FIGS. 10 and 11, the rod 132 andassociated actuating mechanism are replaced by an inflatable bladder150. The bladder 150 is supplied with fluid under pressure throughsuitable means (not shown). Upon inflation of the bladder 150 from thenormal state illustrated in FIG. 10 to the extended state illustrated inFIG. 11, the panel 68 and the knee coil 130 are again raised above theupper major side surface 20 of the table 10. Upon the reduction ofpressure in the bladder 150, the bladder 150 collapses axially to lowerthe panel 68 below the major side surface 20 of the table 10. Thus, theknee joint can also be imaged in a hyper-extended condition.

FIGS. 12-14 illustrate operation of the neck imaging platform 30 of thetable 10. A cervical spine coil 152 is set in the recessed panel portion34 of the table 10, below the upper major side surface 20. Attached tothe head panel 32 is a pivot mechanism 154. A rod 156 has a threadedportion 158 extending through the mechanism 154. Upon rotation of therod 156 by a suitable drive means 160, the actuating mechanism 154causes the head panel 32 to pivot upwardly out of the plane of the majorside surface 20 of the table 10, from the position shown in FIG. 12 tothe position shown in FIG. 13. As shown in FIG. 14 the panel 32 can belowered below the major side surface 20 of the table 10 by rotation ofthe rod 156 in the opposite direction.

With a patient's head lying on the panel 32 and the patient lying on thesurface 20 of the table 10, movement of the panel 32 relative to theupper major side surface 20 of the table 10 causes flexion and extensionof the patient's cervical spine. With the cervical spine coil 152disposed about the cervical spine of the patient, the patient's cervicalspine can be imaged in any selected one of a plurality of positionsthroughout the range of movement of the panel 32. Thus, rather thanbeing limited to one image of the cervical spine while the patient islying flat on an imaging table, the physician can obtain multiple imagesof the cervical spine at various positions throughout its range ofmotion. This is possible with any of the moving parts of the body whichcan be imaged. For example, movement can be measured and controlled indegrees—move a joint 5 degrees, image, move the joint 5 degrees further,image again, etc. Motion can also be measured in distances such ascentimeters between positions.

FIGS. 15-17 illustrate an alternate mechanism for raising and loweringthe panel 32. An inflatable bladder 162 is fixed between the head panel32 and the bottom panel 84 of the table 10. When the bladder 162 is inits neutral condition, the panel 32 is flush with the upper major sidesurface 20 of the table 10. When the bladder 162 is inflated, the panel32 is raised upwardly, out of the upper major side surface 20, to theelevated position illustrated in FIG. 16. When the bladder 162 isdeflated, the panel 32 is lowered below the upper major side surface 20to the depressed position illustrated in FIG. 17. Again, by controllingthe pressure in the bladder 162, the MRI operator can fix the head panelat any given position within its range of motion, in order to image thecervical spine at a selected degree or flexion of extension.

FIGS. 18-20 illustrate the use of the neck imaging platform as modifiedfor imaging an ankle of a patient (not shown). The head panel 32 ismodified by the addition of a foot rest 170. The foot rest 170 issecured to the panel 32 by suitable means. The patient lies on the table10 with, instead of his head at the head end 22, his feet toward thatend. The bottom of the patient's foot is positioned against the footrest 170, with the ankle over the recessed panel 34. An ankle imagingcoil 172 is placed over the ankle. A strap 174 secures the patient'sfoot to the foot rest 170.

When the bladder 162 is in the neutral condition illustrated in FIG. 18,the patient's ankle is in a normal position and may be imaged. Uponfurther inflation of the bladder 162, the panel 32 raises upwardly awayfrom the major side surface 20 of the table 10. The footrest 170 bendsthe patient's ankle and the ankle may then be imaged with the coil 172in that bent condition. Upon the application of suction or lowering ofpressure to the bladder 162 (FIG. 20), the panel 32 is pivoted doombelow the major side surface 20 of the table 10, thus bending the anklein the opposite direction. The ankle may be imaged in that oppositedirection with the secondary coil 172.

FIGS. 21-23 illustrate an alternate actuating mechanism for the ankleimaging platform of FIGS. 18-20. The actuating mechanism is like theactuating mechanism illustrated in FIGS. 12 and 13 for use of the panel32 in cervical spine imaging. Upon rotation of the rod 156 in onedirection or the other, the panel 32 and footrest 170 are pivoted eitherabove the major side surface 20 of the table 10, or below the surface20, to position the ankle for imaging at any selected position withinits range of motion. It should be understood that a separate movableportion of the table 10 could be provided for use in ankle imaging,rather than using the neck imaging platform.

It should also be understood that a table in accordance with the presentinvention need not include every specific movable platform as shownherein. Rather, such a table may include only one movable platform, orany combination of various movable platforms. It should further beunderstood that suitable control means is provided for moving theseveral platforms, in a known manner, in order to provide repeatablemovement of the various platforms through their respective ranges ofmotion, in order to provide repeatable imaging at known positions. Thetable can also be used, of course, for other types of imaging such asultrasound or CAT scans. It should further be understood that any of theplatforms may be provided as separate devices which can be placed atop aknown imaging table, rather than being built into a new table as shown.

Accordingly, it is seen that the present invention provides an imagingtable for positioning a body part so as to control the position ororientation of the body part. This positioning is independentlycontrollable by the operator from a location external to the primarycoil. This positioning requires no physical support effort by thepatient during the time period of the imaging to maintain the selectedposition, as the table fully supports the weight of the body partconnected therewith. Accordingly, a plurality of sequential images maybe taken of a joint, for example, in differing positions, without undueeffort on the part of the patient.

In another embodiment of the invention, FIGS. 24-26 illustrate anapparatus 200 for positioning a body part within a primary imaging coil.The apparatus 200 is mounted to an imaging table 202 which may be theimaging table 10 or may be a known imaging table. A known secondaryimaging coil 204 is secured to the table 202 by suitable means. The coilis located in a position for imaging a particular body part. Asillustrated in FIGS. 24 and 25, the coil 204 is positioned to image ashoulder of a patient who is lying on the table 202 with his headadjacent the end 206 of the table 202.

The apparatus 200 includes a support rod 210 extending longitudinallyalong the table 202 from a position over the table 202 (inside theprimary coil) to a position off the end of the table 202 (outside thecoil). The rod 210 has an inner end portion 212 to which is fixed anattachment member 214. The member 214 may be any suitable structure suchas a cuff for attachment to a body part such as a forearm, for example,and may include means (such as the straps 215) for securing the cuff tothe body part for movement therewith. The rod 210 also has an outwardend portion 216 to which is attached a handle 218 for rotational andlongitudinal movement of the rod 210 by a person other than the patient(not shown).

The rod 210 extends through and is positioned by an index mechanism 220,better seen in FIG. 26. The index mechanism 220 includes a base 222having a first leg portion 224 and a second leg portion 226. The legportion 224 is fixed to the table 202. The leg portion 226 has an uppermajor side surface 228 to which are attached support blocks 230 and 232.The support block 230 has an opening 234 through which the rod 210extends and is movable. The support block 232 has an opening 236,aligned with the opening 234, through which the rod 210 also extends andis movable. The blocks 230 and 232 support the rod 210, and thus thecuff 214. The block 232 also has a plurality of index openings 238. Theindex openings 238 are spaced regularly in a circle around the rod 210.

An index block 240 is disposed on the rod 210 outside the block 232. Therod 210 extends through an opening 246 in the index block 240. The indexblock 240 includes a split clamp portion 242 and a clamping bolt 244.When the split clamp 242 is loosened, the index block 240 is rotatableon and movable longitudinally on the rod 210. When the split clamp 242is tightened, the block 240 is fixed for movement with the rod 210.

The index block 240 has an index pin opening 250 through which isextensible an index pin 252. The opening 250 is the same distance fromthe center of the opening 246, as the index openings 238 are from thecenter of the opening 236 in the block 232. Thus, the index pin opening250 is alignable with any selected one of the index openings 238 on thesupport block 232. When the opening 250 is aligned with one of the indexopenings 238, the index pin 252 may be inserted through the index pinopening 250 and into the selected index opening 238, to block rotationof the index block 240 relative to the support block 232. If the indexblock 240 is clamped firmly to the rod 210, this blocks rotationalmovement of the rod 210 relative to the support block 232. Since thesupport block 232 is fixed to the table 202, this therefore blocksrotational movement of the rod 210 relative to the table 202, also thusfixing the cuff 214 in position. Further, when the index pin 252 isextended through the index pin opening 250 and into one of the indexlocations 238, the index assembly 220 blocks longitudinal movement ofthe rod 210 relative to the table 202. Thus, the cuff 214 is completelyfixed in position relative to the table 202 and the coil 204.

It should be noted that other indexing mechanisms may be provided toreplace the index pin opening 250 and index pin 252. For example, asshown in FIG. 26A, the index block 240 may have a spring loaded ball 254on its radially outer surface facing the support block 232, which isselectively engageable at one of a plurality of ribbed index locations256, thus functioning as a detent mechanism. This is suitable for apatient-directed operation. If the apparatus 200 is to be patientdirected, the portion of the rod 210 extending outwardly past the indexmechanism 220 may be omitted. The patient adjusts the index mechanism bymoving the body part, thus moving the cuff and support rod. Other indexconstructions are equally feasible.

In operation of the positioner apparatus 200, the patient is firstplaced on the table 202 in a position as desired. The coil 204 isadjusted so as to properly image the body part in question. (It shouldbe noted that use of a secondary coil such as the coil 204 is notessential to functioning or use of the apparatus 200.) The cuff 214 isthen attached to a portion of the patient's body at a location selectedto be able to move the body part to be imaged into a plurality ofdifferent positions. For example, if a shoulder joint is to be imaged,then the cuff 214 may be attached to the patient's forearm. Movement ofthe patient's forearm by means of the rod 210 will then cause theshoulder joint to move between a plurality of different positions.Similarly, if the patient's hip is to be imaged, the cuff 214 may beattached to the patient's leg, for example, the lower leg. Movement ofthe cuff 214 will cause movement of the hip joint to a plurality ofdifferent positions in which it may be sequentially imaged.

The rod 210 as noted is longitudinally movable by pulling or pushing onthe handle 218. Thus, as the imaging operator moves the handle 218longitudinally relative to the table 202, the cuff 214 thus moveslongitudinally also. The operator can therefore control the longitudinalposition of the cuff 214, and of its attached body part, from a locationexterior to the primary coil.

The rod 210 is also rotatable, by means of the handle 218. The operatorrotates the handle 218 to position the cuff 214 and its attached bodypart in the desired orientation for imaging. This rotational position isthen locked in by means of the index assembly 220. It should be notedthat any number, location, or sequence of index locations 238 may beprovided. Those shown are illustrative only. In fact, an index assemblymay be provided which can be locked in any rotational position within afull circle.

Many joints are movable in multiple degrees of freedom. The shoulderjoint, for example, is movable in four degrees of freedom (or multipleplanes of movement). In order to fully understand the joint anatomy, itis desirable to be able to image a joint in all these possiblepositions. Accordingly, the present invention provides for movement of apositioning apparatus such as the cuff 214 not merely rotationally andlongitudinally, but also up and down and sideways.

Thus, as seen in FIGS. 24-26, the apparatus 200 may be made movable upand down and also sideways relative to the table 202. The index blocks230 and 232 are movable up and down along rods 231 and 233,respectively, which rods are fixed to the base block 222. Thus, thesupport rod 210 and cuff 214 can be moved up and down to provide a thirddegree of movement in addition to the rotation and longitudinal movementavailable. Further, the index assembly 220 has a guide member 235engaging in a slot 237. Thus, the index assembly is movable sidewaysalong the table 202 to carry the support rod 210 and the cuff 214 in afourth degree of movement. With these multiple degrees of movement, inmultiple planes, it is now possible to move a joint into almost anyposition to simulate natural joint movement, while within an imagingcoil.

Another feature of the present invention is that traction can be appliedto a joint being imaged, in order to distract the joint. For example, inthe apparatus illustrated in FIGS. 24-26, traction can be applied to ajoint by pulling outwardly (to the right as viewed in FIG. 24) on therod 210. Such force when applied to the rod 210 acts through the cuff214 on the joint being imaged. Distracting a joint can allow a betterview of the parts of the joint and thus an increased imaging benefit.This feature is not available with present imaging apparatus.

It should be noted that additional body part attachments are possible inorder to better control movement and positioning. For example, extracuffs or clamps, in addition to the one cuff shown in the drawings, maybe attached to the body to more carefully and tightly control itsmovement and positioning. Further, it should be understood that othertypes of cuffs may be used, such as inflatable cuffs, etc. The cuffsshould further be designed so that there is no plastic in contact withthe skin. Such contact causes sweating and perspiration build up whichcauses imaging aberrations. Accordingly, a material is preferablyprovided against the skin to wick the perspiration away.

Accordingly, it is seen that the present invention provides an apparatusfor longitudinally and rotationally positioning a body part so as tocontrol the position or orientation of a joint connected with the bodypart. This positioning is independently controllable by the operatorfrom a location external to the primary coil. This positioning requiresno physical support effort by the patient during the time period of theimaging, since the rod positioning apparatus fully supports the weightof the body part connected therewith. Nor does this adjustablepositioner require any effort on the part of the patient to maintain theselected position, as the apparatus 200 performs that function also. Aplurality of sequential images may be taken of a joint, for example, indiffering positions, without undue effort on the part of the patient.(It should be noted that patient control of any of the positioningapparatus of the present invention is possible, as well as the describedoperator control.)

FIGS. 27-29 illustrate another body part positioner having two degreesof movement. An apparatus 260 includes a saddle 262 having upstandingside portions 264 and 266 joined by a bottom portion 268. The saddle 262is mounted on a base block 270. The base block 270 is mounted on a panel272 which may be the head panel 32 of the table illustrated in FIG. 1A.The panel 272 has a plurality of index openings 274. An index pin 276(FIG. 27) extends through a portion 278 of the base block 270 and isreceivable in a selected one of the openings 274. The base block 270 ispivotally mounted at 280 to the panel 272. Thus, the base block 270,with its attached saddle 262, may be positioned at a selected one of aplurality of rotational positions relative to the panel 272, as shown inphantom in FIG. 27.

An index plate 282 is attached to the saddle 262. The index plate 282and saddle 262 are pivotally mounted at 284 to the base block 270. Theindex plate 282 has a plurality of index openings 286 spaced in an arcabout the pivot mounting 284. A locator opening (not shown) is locatedbehind the index plate 282, in the base block 270. The saddle 262, withits attached index plate 282, may be pivotally rotated about themounting 284, as shown in phantom in FIG. 28, and secured in a positionby insertion of an index pin (not shown) through the selected opening286 into the locator opening in the base block 270.

In operation of the positioning assembly 260, the patient's head issecured in the saddle 262. The saddle 262 and base block 270 are thenswung around the pivot axis 280 and locked in a selected position withthe index openings 274. The saddle 262 is also rotated, with the indexplate 282, about the pivot axis 284 and locked in a selected position.The patient's head or cervical spine is then imaged. The apparatus 260is then adjusted to a different condition, moving the patient's head orspine to a new position. The patient's head or spine is then imagedagain.

Accordingly, it is seen that a patient's head or cervical spine, whenthe head is in the saddle 262, can be selectively positioned in any oneof a plurality of different orientations within two separate degrees ofmotion. Further, if the head panel 272 is pivotally mounted to the table10, the attached saddle 262 may also be moved up and down out of theplane of the table, thus moving the patient's head in the saddle 262 inyet a third degree of motion. The control of all these movements may beautomated with a fluid drive or other means, may be made remotelycontrollable from a location outside the coil, or may be patientdirected.

Accordingly, it is seen that the present invention also providesapparatus for positioning a body part of a patient for imaging in aplurality of different degrees of motion. For example, the patient'scervical spine may be imaged in a sequence of images by moving thesaddle 262 in the desired direction within the various degrees of motionand locking it in place at each selected position. There is no need forthe patient to hold any selected position, as the positioning apparatus260 does this for him. Accordingly, the imaging process is madesignificantly more stable and more comfortable for the patient.

Because coil support panels such as the recessed panels 34 and 48 (FIG.1A) are located below the upper major side surface 20 of the table 10, aflat surface coil placed therein will not interfere with normal bodypositioning. Thus, it is seen that recessing the coils, itself, providesa significant benefit.

Several patient directed devices are illustrated in FIGS. 30-40. Suchdevices can be part of a new imaging table as described above, but canalso be independent, that is, add-ons to an existing imaging table (asthe apparatus 200 is an add-on to the table 202 in FIGS. 24-26). Theyare therefore less expensive and more widely usable.

These patient-directed devices can be end-mounted fixtures such as amodification of those shown in FIGS. 24-26. They can also be fixturesmounted to the upper surface of the table, in effect replacing themovable platforms of the table of FIG. 1A.

FIGS. 30-36 illustrate a patient directed wrist movement apparatus 300.The apparatus 300 includes a base 302 which may be secured to an imagingtable with suitable means not shown. The base 302 supports an imagingcoil 304. The patient's forearm is placed on a forearm cuff 306 securedto the base 302. The patient's hand is placed, thumb up as seen in FIG.33, in a hand cuff 308. The hand cuff 308 is pivotally mounted at 310 tothe base 302. A detent member 312 is located on a lower end portion 314of the hand cuff 308. The detent member 312 is engageable with aratchet-type member 316 on the base 302. Thus, the hand cuff 308 and thebase 302 are releasably interlockable at a plurality of positions withintheir range of rotational movement.

To adjust the apparatus 300, the patient simply applies sufficienttorque to release the interconnection between the hand cuff 308 and thebase 302 and thereby flex or extend his wrist to the next desiredposition. The apparatus 300 then interlocks at this newly selectedposition for imaging by the coil 304.

A modification of the apparatus 300 is illustrated in FIG. 32 with anapparatus 320 having a different hand cuff 322. The hand cuff 322 isdesigned to have the hand lie flat rather than on edge, with the thumbto the side as viewed in FIG. 32. The wrist is again movable through itsrange of motion, this time being imaged in a position 90.degree. fromthat shown in FIG. 30.

FIGS. 37-40 illustrate a patient directed knee imaging apparatus 330.The apparatus is similar to the knee platform of the table 10 of FIG.1A, but is instead designed to be patient directed (actuated) ratherthan technician or operator directed.

The apparatus 330 includes a base 332. The base 332 rests on the uppermajor side surface of the table. Suitable means may be provided tosecure the base 332 to the table. A lower leg cuff 334 is releasablysecured to the lower leg. The cuff 334 is attached at 336 to the base332 to maintain the same focal point of imaging as the knee is flexed.An upper leg cuff 338 is releasably secured to the upper leg. The upperleg cuff is also attached at 340 to the base 332.

A knee imaging coil 342 is fixed for movement with a movable panel orportion 344 of the base 332. Attached to the patient's foot is afootrest 346 with a pawl member 348. The pawl member 348 engages aratchet portion 350 on the base 332.

To adjust the device, the patient simply bends his knee to move his footand thus the pawl member 348 along the ratchet portion 350 from oneposition to the next. The panel 344 moves in a manner as describedabove. The patient's foot is then held in that position firmly enough toallow for accurate imaging.

As the patient moves his foot and knee, the secondary coil 342 moveswith the knee and generally stays in position relative to the knee. Thesecondary coil 342 is constrained for movement by the panel 344 so thatit stays in the proper planar orientation relative to the primaryimaging coil (not shown). As the patient moves his foot and knee, thecuffs 334 and 338 are constrained for proper movement by the mechanismswhich attach them to the base 332 in order to maintain the same focalpoint of imaging as the knee is flexed. The coil 342 stays in closeproximity to the knee, moves longitudinally and up and down as the kneemoves, and maintains its proper planar orientation throughout its rangeof motion.

An optional addition to the apparatus 330 is a distraction member 352(FIG. 40). As illustrated the distraction member 352 is an inflatablebladder having a bellows-type construction for support. The bladder 352extends between the lower leg panel 354 and the lower leg cuff 334. Whenthe bladder is inflated, it applies force to push the lower leg up tostress the knee outwardly. This can be done to check ligaments in theknee for damage or weakness. This feature of distraction or stressing ofa joint can be applied in other joints, on other positioning apparatus,and to move body parts in an manner needed to simulate natural loadingof a joint or to enable better imaging of the joint under variousconditions.

Thus, it is seen that the present invention provides apparatus for usein imaging which can be attached to an existing table, allows thepatient to direct the movement, controls the motion of the joint in arepeatable manner, moves a secondary coil with the joint, and holds thesecondary coil in proper alignment. Of course, the movement can beoperator controlled, also, by using, for example, a rod attached to thepawl device for moving the patient's foot. Similar constructions asmodified can be used to provide for patient directed movement of otherbody parts and joints.

If a joint is small enough and/or limited enough in its range of motionthat imaging the joint with one fixed secondary coil provides acceptableresolution, then it may not be necessary to move the secondary coil. Forexample, the wrist is a relatively small joint which, even when movedthrough its entire range of motion, does not take a large amount ofspace. Thus, the wrist is imaged using flat plates on either side of thewrist or a coil extending around the wrist.

An example of these features is the patient directed apparatus 300(FIGS. 30-36) for moving the wrist through its range of motion withinfixed coils. Similarly, the shoulder is a joint which does not movesignificantly through space when bent. Accordingly, it can usually beimaged successfully using a fixed coil. In this case, the presentinvention provides the fixture 200 (FIGS. 24-26) for moving the shoulderthrough its range of motion within the fixed coil.

However, some joints are large enough and/or move through space so thatit is impossible to obtain optimum resolution with a fixed secondarycoil through the entire range of motion of the joint. In this case, thepresent invention provides fixtures for moving the secondary coil withthe joint. An example is the movable knee platforms of the table of FIG.1A. Another example is the apparatus of FIGS. 37-40 for imaging the kneein a patient directed manner with a moving secondary coil.

It should be understood that the present invention contemplates the useof drive or actuating mechanisms other than those shown. For example,any one of the movable portions of the apparatus shown could be drivenby a piston-cylinder device which is pneumatic or hydraulic. A pneumaticmotor drive could be used, as well as an electric motor drive.Similarly, the pawl and ratchet or detent mechanisms illustrated inFIGS. 30-40 could be used in other configurations, as they areespecially suitable for precise, repeatable incremental motion control.

In this regard, reproducability of the movement is desirable so that thepatient's progress over a period of time can be checked. Thus, indexingmovement of the body part being imaged through degrees or distance isadvantageous. Reproducability, as provided by the present invention, isalso useful in conducting clinical studies of groups of patients.

In accordance with the present invention, it is possible to use a largerdiameter primary coil, allowing increased range of limb movement,without the degradation in image quality which would be expected fromthe increased coil size. This is possible because of total imagingavailable with the extensive use of secondary coils as described herein.For example, the knee could be flexed through its entire range of motionto allow optimum imaging of the knee joint. This is currently impossiblewith the known small primary coils which only allow about 50 degrees offlexion.

Thus, as illustrated in FIG. 41, a known primary MRI coil 360 with atable 362 has a height 361 from the table to the inside of the coil of16″. The table 362 has a width 363 of 19″. As illustrated in FIG. 42, areplacement primary MRI coil 364 in accordance with the presentinvention, with a table 366, has a height 365 from the table to theinside of the coil of 21.5″. The table has a width 367 of 24″. Withthese dimensions and the moving secondary coils, substantially increasedlimb movement is possible, without degradation of image quality.

In a further embodiment of the present invention, an MRI primary coil ismounted to extend vertically rather than horizontally. Thus, asillustrated in FIG. 43, a primary MRI coil 368 extends vertically ratherthan horizontally. A patient may be placed in a standing or seatedposition on a support 370 for imaging in the coil 368. A ram 372 isoperable to move the patient into and out of the coil 368. Positioningfixtures, etc. are mounted to a support member 374.

With the patient in a vertical or in a seated position, it is possibleto simulate joint positionings and joint loadings which can not readilybe simulated when the patient is lying down in a known horizontalimaging coil. For example, a weight or other tractive force can beattached to the arm to simulate shoulder joint loading experienced whencarrying a heavy object. The knee can be imaged with the patientstanding to see how the joint appears when loaded with body weight. Thespine can be imaged when standing or seated to check for disc orvertebral problems which are experienced in normal life but whichdisappear when the patient lies down to be imaged in a known horizontalimaging coil. The possibilities for increased usefulness of the imagingmethodology are manifold.

Any of the positioning apparatus disclosed herein are usable with orwithout a secondary coil. When used with a secondary coil, they providethe benefit of constraining movement of the secondary coil in a properplanar orientation relative to the primary coil, and also the benefit ofkeeping the secondary coil in close proximity to the body part beingmoved and imaged.

If the various apparatus of the present invention are used for magneticresonance imaging, they must be made of non-ferromagnetic materials.Plastic is preferred for the table and the positioner, while brass issuitable for mechanical drive mechanisms. Fluid drive mechanisms arealso highly suitable because they can be easily constructed usingplastic components. Wood is also usable.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications in the invention.Such improvements, changes and modifications within the skill of the artare intended to be covered by the appended claims.

1. A magnetic resonance imaging system comprising: a stationaryelectromagnet; a patient support located adjacent to the electromagnet,the support configured for maintaining a patient in a standing position;and an actuator for raising and lowering the patient support and patientrelative to a magnetic field of the electromagnet such that the patientis located within the magnetic field.
 2. A magnetic resonance imagingsystem as defined in claim 1 further including at least one positioningfixture connected with the patient support for maintaining the patientin the standing position.
 3. A magnetic resonance imaging system asdefined in claim 2 further including at least one secondary coilpositioned within the magnetic field of the stationary electromagnet. 4.A magnetic resonance imaging system comprising: a stationaryelectromagnet having a longitudinal axis extending generally vertical; apatient support located adjacent to the electromagnet for maintaining apatient in a seated position; and an actuator for raising and loweringthe patient support and patient relative to a magnetic field of theelectromagnet such that the patient is located within the magneticfield.
 5. A magnetic resonance imaging system as defined in claim 4further including at least one positioning fixture connected with thepatient support for maintaining the patient in the seated position.
 6. Amagnetic resonance imaging system as defined in claim 5 furtherincluding at least one secondary coil positioned within the magneticfield of the stationary electromagnet.
 7. An apparatus for magneticresonance imaging of a joint of a patient, the apparatus comprising: astationary electromagnet; a patient support located adjacent theelectromagnet, the support configured for maintaining a patient in astanding position, whereby a first force is applied to the joint; atleast one positioning fixture connected with the patient support forholding the joint of the patient; and an actuator for raising andlowering the patient support and patient relative to a magnetic field ofthe electromagnet such that the joint of the patient is located withinthe magnetic field.
 8. An apparatus as defined in claim 7 furtherincluding means for applying a second force to the joint.
 9. Anapparatus for magnetic resonance imaging of a joint of a patient, theapparatus comprising: a stationary electromagnet having a longitudinalaxis extending generally vertical; a patient support locate adjacent tothe electromagnet for maintaining a patient in a seated position,whereby a first force is applied to the joint; at least one positioningfixture connected with the patient support for holding the joint of thepatient; and an actuator for raising and lowering the patient supportand patient relative to a magnetic field of the electromagnet such thatthe joint of the patient is located within the magnetic field.
 10. Anapparatus as defined in claim 9 further including means for applying asecond force to the joint.
 11. An apparatus for magnetic resonanceimaging of a spine of a patient, the apparatus comprising: a stationaryelectromagnet; a patient support located adjacent to the electromagnet,the support configured for maintaining a patient in a standing position,whereby a first force is applied to the spine; at least one positioningfixture connected with the patient support for holding the spine of thepatient; and an actuator for raising and lowering the patient supportand patient relative to a magnetic field of the electromagnet such thatthe spine of the patient is located within the magnetic field.
 12. Anapparatus as defined in claim 11 further including means for applying asecond force to the spine.
 13. An apparatus for magnetic resonanceimaging of a spine of a patient, the apparatus comprising: a stationaryelectromagnet having a longitudinal axis extending generally vertical; apatient support located adjacent to the electromagnet for maintaining apatient in a seated position, whereby a first force is applied to thespine; at least one positioning fixture connected with the patientsupport for holding the spine of the patient; and an actuator forraising and lowering the patient support and patient relative to amagnetic field of the electromagnet such that the spine of the patientis located within the magnetic field.
 14. An apparatus as defined inclaim 13 further including means for applying a second force to thespine.
 15. A method for magnetic resonance imaging, the methodcomprising the steps of: positioning a patient against a patient supportconfigured for maintaining the patient in a standing position; movingthe patient into a magnetic field of a stationary electromagnet; andimaging the patient with the electromagnet.
 16. A method as defined inclaim 15 further including the step of using at least one positioningfixture to maintain the patient in a generally fixed position beforeimaging the patient with the electromagnet.
 17. A method as defined inclaim 15 wherein the step of imaging the patient with the electromagnetincludes imaging the patient with the stationary electromagnet and asecondary coil.
 18. A method for magnetic resonance imaging, the methodcomprising the steps of: positioning a patient against a patient supportsuch that the patient is maintained in a seated position; moving thepatient into a magnetic field of a stationary electromagnet having alongitudinal axis extending generally vertical; and imaging the patientwith the electromagnet.
 19. A method as defined in claim 18 furtherincluding the step of using at least one positioning fixture to maintainthe patient in a generally fixed position before imaging the patientwith the electromagnet.
 20. A method as defined in claim 18 wherein thestep of imaging the patient with the electromagnet includes imaging thepatient with the stationary electromagnet and a secondary coil.